/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head)
    {

        return dfs(head, nullptr);
    }

    ListNode* dfs(ListNode* cur, ListNode* prev)
    {
        if (cur == nullptr)
        {
            return prev;
        }
        ListNode* head = dfs(cur->next, cur);
        cur->next = prev;


        return head;

    }
};